Direct current motors are used today in many technological fields, such as in automotive technology for powering a fan wheel of a cooling blower. The supply voltage of the direct current motor is clocked as a rule by means of an FET, which is directed according to the PWM method. Through modification of the touch proportions in use, that is, the proportions between pulse width and the length of pulse pauses, the terminal voltage on the terminals of the direct current motor can be changed, so that the current consumption of the motor and thus the torque of the drive can be modified.
To recognize disturbances and damage of the described drive system, the motor current is recorded. For instance, the color wheel can become jammed by leaves, leading to excess current and to heating and destruction of electronic components. In addition, it can result in a short-circuit, which can likewise cause damage to the drive system.
In embodiments of cooling drives commonly known in the state of the art, the current was recorded, for instance, by a shunt resistance, with the disadvantage that it can result in voltage loss.
U.S. Pat. No. 5,204,594, for instance, describes a brushless DC motor in which a shunt resistance is used in connection with an operating amplifier to record the current. Here too the result can be additional losses from the shunt resistance. In addition, the described solution is cost-intensive because an additional amplifier must be used.
It is the aim of the current invention therefore to provide an improved method and an improved switching apparatus for recording current in an electrical device, which apparatus is directed according to the pulse width modulation method by a field effect transistor that is coupled with the device, so that the method and apparatus entail fewer losses and can be produced in simple and cost-effective manner.